Based on the CGI renders, the details on HA Bumblebee's legs are facing the wrong way. So I tried tinkering with him and found a simple mod. Basically, you will need to disassemble his crotch and re-assemble it backwards. After that (during transformation), rotate the waist while at the same time rotating the hips part:

STEPS

Step 1 - Transform Bee's legs as normal and leave the upper body in car mode
Step 2 - Just shows what the crotch and leg parts look like out of the box
Step 3 - Disassemble the crotch pieces (Remove 2 screws from behind)

Step 4 - Reassemble the crotch pieces backwards (Compare the pics for Steps 2 and 4 to see the difference)

Step 5 - Lift up the leg to its side
Step 6 - Rotate 180 degrees at the hip joint

Step 7 - Bring the leg down (See pic)
Step 8 - Before rotating the waist angle the legs abit as shown in the pic
Step 9 - Rotate at the waist joint

NOTE: Adjust the angle of the legs and the thigh parts while rotating the waist. There is a certain angle where it will allow you to rotate the whole waist smoothly.

(This modification proved to be very popular, and much discussion took place after len_d69 originally posted it. The useful portions pertaining to the modification that len_d69 demonstrates are retained below. ~Superquad7)

shadow panther said:

From car mode, transform the feet out first. This way there is more clearance to rotate the waist but make sure that you rotate the hips part as well (See the difference in the attached pic - inside red square).

Click to expand...

plowking said:

Actually you can try this transformation first before disassembling anything. What will happen is that the crotch piece will be facing the wrong direction in bot mode because of the waist rotation.

Click to expand...

The best way to do the mod is to swap the crotch pieces and not touch the legs. Reason is that if you try swapping legs you might end up with a non transformable figure. Here are before and after shots.

Crotch Swap - Easier and suggested way (NOTE: You will need to rotate the waist and hips after the mod to transform to bot mode)

Leg Swap - Need to take note of the hip joints. They are alot lower after the mod compared to the original position.

Which ever way you use, it will still end up the same.

Here's a very useful video by Peaugh explaining the mod and how to make clearance to rotate the waist and hips
(Starts off at 00:48 sec)